SPRDSenior Physics Research DatabaseDickinson College

All projectsDirectional speaker

Measurement

Beam measurements

Record the speaker playing a 1 kHz tone and measure how loud and how distorted the audible sound is against distance and angle.

Week 3 of 4; the paper is due at the end of week 4

Goals

  • Measure the 1 kHz level on axis against distance, the same quantity the KZK simulation predicts.
  • Measure the level against angle at a fixed distance to show how narrow the audio beam is.
  • Measure the harmonic distortion of the 1 kHz tone (the 2 kHz and 3 kHz lines) and compare it with the simulated value.

Why this matters

These are the Results of your paper. A few clean, repeatable curves with honest error bars are worth more than a big pile of single readings.

The physics

What to expect, from the earlier steps:

  • On axis, the audio first grows with distance as the virtual end-fire array builds up, then decays.
  • Off axis, the audio drops quickly, much faster than an ordinary loudspeaker playing the same tone.
  • The demodulated audio is distorted. For a 1 kHz tone, the spectrum of your recording shows lines at 2 kHz and 3 kHz as well. The total harmonic distortion is
THD=A22+A32+A42+…A1,\mathrm{THD} = \frac{\sqrt{A_2^2 + A_3^2 + A_4^2 + \dots}}{A_1},

where AnA_n is the amplitude of the line at n×1n \times 1 kHz. The simulation prints the same number, so the two can be compared directly.

Hints

Hint 1Play exactly what you simulate

Feed the speaker a pure 1 kHz tone from any tone generator, or write one with a few lines of numpy and scipy.io.wavfile. Then the simulation’s 60 kHz carrier modulated by 1 kHz and your measurement describe the same signal, apart from what the speaker does internally.

Hint 2Repeat one measurement many times first

Before scanning, take the same reading ten times, moving the microphone away and back each time. That spread is your real uncertainty, and it is usually bigger than the meter’s resolution.

Hint 3Record the background and the room

Record with the speaker off to get the noise floor at 1, 2 and 3 kHz. Write down temperature and humidity too: the absorption of the carrier depends on them, and the simulation needs them.

Hint 4Watch for reflections

Walls and tables reflect the beam like a mirror. Measure at one point with and without absorbing material nearby to see how big the effect is.

Hint 5Keep the raw recordings

Save the WAV files, not only the dB values. You will want to redo the analysis once you know more.

What past teams did

2026–27 team

First team on the project. Add your data files (or a link to them) and a short description of each.